A conventional radiation image conversion panel containing a stimulable phosphor layer prepared by a gas phase accumulation method has a columnar crystal in the phosphor layer. Since this type of radiation image conversion panel contains no binder resin, there are formed spaces between one columnar crystal and other columnar crystals. Therefore, diffusion of an excitation light can be prevented and improvement of a taking out efficiency of an emitting light can be achieved, which results in obtaining an image of high luminance and high sharpness.
However, this radiation image conversion panel has a problem of easily deteriorating during storage because it contains no binder, and as a result, the surface of the phosphor is exposed. It was needed to figure out a way such as surface treatment and lamination to avoid contact with the outside air as much as possible.
Even though the performance degradation as a product can be prevented, unlike the inner portion of a crystal, the surface and the side of the phosphor crystal basically prepared by a gas phase accumulation method are placed under various environmental conditions in the processes from vapor deposition to sealing.
For example, during the vapor deposition process, there are factors such as vacuum atmosphere, change of a temperature and adsorption and desorption of an inert gas. And during the subsequent processes, there are factors caused by a surface treatment and influences of water in the atmosphere. Thereby, there was a problem that a content of an activating agent tends to be different between the surface and the inner portion of the crystal.
Moreover, about the surface state of the phosphor crystal, which seems to have an important role on performance of the phosphor, there have been disclosed very limited reports until now. There was disclosed only a report in which a ratio of Cs and C was specified (for example, refer to Patent Document 1). The purpose of this disclosure is to decrease contamination on the crystal surface and this differs from the present invention in that it is not an investigation of a distribution of an activating agent concentration.
Patent Document 1: JP-A 2005-24272